The invention relates to a fluid feed duct, which is suitable particularly for recirculating exhaust gas into the intake system of an internal combustion engine.
The recirculation of exhaust gases into the intake tract of an internal combustion engine is known in the art. This measure is taken to reduce the emission of harmful pollutants from the internal combustion engine. A problem, however, is the high temperature of the exhaust gas. Particularly if the intake tract is made of thermoplastic synthetic resin material, the introduced exhaust gas can cause the intake tract to melt in the area of the exhaust gas feed.
To prevent thermal overstressing of the intake tract, EP 486,338 proposes a double wall design for the exhaust gas feed duct. The exhaust gas is fed through the inside pipe into the intake tract. The hollow space resulting between the double wall has an insulating effect with respect to the junction between the exhaust gas feed duct and the intake pipe.
To achieve an additional cooling effect, a portion of the fresh intake air is guided through this gap. The fresh intake air is removed from a point in front of a throttle valve and reaches the gap via a bypass line. The cooling air returns to the intake tract through corresponding openings parallel to the exhaust gas stream.
This proposed solution, however, does not allow the proportion of recirculated exhaust gas to transmitted combustion air to be increased at any desired ratio. The double-walled pipe is connected directly with the intake pipe, so that at higher recirculation rates, there is nevertheless a risk that the wall of the intake tract may melt. Also, the hot exhaust gas stream directly strikes the opposite wall of the intake tract, which creates another area of high thermal stressing and may cause the component to fail.
To prevent this, the design proposed in EP 886 063 A2 provides a gas conduction element 26 (cf. FIG. 2), which can withstand the thermal stress and protects the wall of the intake tract against direct impingement of the hot exhaust gas stream. Within this gas conduction element the hot exhaust gas stream has sufficient time to mix with the intake air. However, such an additional component increases the design complexity as well as the weight of the intake tract. Both are undesirable in view of the greatest possible economic efficiency, which is the aim in the production and the use of the intake tract.
To obviate these drawbacks, the Automobiltechnische Zeitschrift, Volume 1992, p. 530 proposes to fasten hot pipes to plastic components. This hot pipe is again a double-walled pipe, but the inner pipe ends earlier than the outer pipe. This achieves an ejector effect, so that cooling air from the intake tract can be sucked through the gap of the double-walled pipe. Thus, the intake point is cooled and the cooling air simultaneously mixes with the exhaust gas stream and thereby cools the exhaust gas.
Even in this exhaust gas recirculation design, however, the realizable exhaust gas recirculation rates have an upper limit. To make the cooling gas stream possible, it is necessary to mount the exhaust gas recirculation pipe on a collar that merges directly into the locating flange for the exhaust gas feed duct on the intake manifold. At high exhaust gas recirculation rates, this heat bridge causes excessive thermal stressing of the intake tract in the area of the exhaust gas recirculation. Moreover, although the exhaust gas stream is being cooled, a gas guidance element in accordance with EP 886 063 must be provided in the intake tract if a certain exhaust gas recirculation rate is exceeded.
Thus, the object of the invention is to provide a fluid feed duct for conducting hot fluids into a hollow structure for transmitting a cooler fluid.
Another object of the invention is to provide a fluid feed duct arrangement which is cost effective to produce.
A further object of the invention is to provide a fluid feed duct which permits a high rate of introduced hot fluid in proportion to the transmitted fluid, while maintaining the thermal stressing of the hollow structure within the required limits.
These and other object of the invention are achieved by providing a fluid feed duct for recirculating engine exhaust gas into an intake tract of an internal combustion engine comprising a hollow structure for transmitting a fluid from an inlet to an outlet; a feed connection projecting interiorly into the hollow structure for introducing into the hollow structure a fluid that is hotter than the transmitted fluid, and a joint structure for sealingly mounting the feed connection inside the hollow structure, in which the feed connection and the joint structure have greater heat resistance than the hollow structure; the feed connection is heat-resistant to the introduced fluid; an end area of the feed connection points in the flow direction of the transmitted fluid, and sides of the end area around which the transmitted fluid flows are provided with outlets opening into the interior of the hollow structure.
In accordance with a further aspect of the invention, the objects are also achieved by providing a fluid feed duct for recirculating engine exhaust gas into an intake tract of an internal combustion engine comprising a hollow structure for transmitting a fluid from an inlet to an outlet; a feed connection for introducing into the hollow structure a fluid that is hotter than the transmitted fluid, and a joint structure for sealingly mounting the feed connection inside the hollow structure; wherein the feed connection and the joint structure have greater heat resistance than the hollow structure; the feed connection is heat-resistant to the introduced fluid, and means are provided to reduce the heat transfer from the feed connection to the joint structure.
According to the invention, the feed connection of the feed duct in the end area extending into the interior of the hollow structure is provided with outlet openings pointing in the flow direction of the transmitted fluid. This design measure causes the flow of the introduced fluid to be diverted in flow direction inside the hollow structure, which prevents the introduced fluid stream from striking a wall of the hollow structure. Using the ejector effect, the introduced fluid is caught and entrained by the flow of the transmitted fluid, so that rapid mixing occurs. This mixing simultaneously cools the introduced fluid and heats the transmitted fluid. The resultant temperature, however, falls within the range of the permissible thermal stressing of the hollow structure wall.
The outlet openings are arranged along the sides in the end area of the feed connection. The fact that there is a plurality of these openings enhances the mixing effect since the stream of the introduced fluid is broken up into many small partial streams.
In accordance with a further embodiment of the invention, the outlet openings are provided with baffles. Particularly if the feed connection is made of sheet metal, these baffles can be simply produced by stamping. The baffles are preferably bent into the interior of the feed connection and thereby cause optimal mixing of the introduced fluid with the transmitted fluid. In addition, the baffles cause the introduced fluid to be injected as it exits along the end area of the feed connection, so that direct contact of the introduced fluid with the walls of the hollow structure is avoided. This contact occurs only after a sufficient mixing path in the continued course of the transmitted flow inside the hollow structure.
To further promote the mixing of the two fluids, it is advantageous to provide the feed connection with a flow-optimized outer contour relative to the transmitted flow inside the hollow structure. As the fluid flows around the feed connection, a laminar flow is then created along the outer contour of the feed connection, particularly its end area. This improves the mixing result with the introduced fluid.
A particularly advantageous embodiment of the fluid feed duct is obtained if the end area of the feed connection points in the flow direction of the transmitted fluid and the sides of this end area are provided with outlet openings opening into the interior of the hollow structure around which the fluid flows, and if preferably ceramic means also are provided to reduce the heat transfer from the feed connection to the joint structure which sealingly mounts the feed connection inside the hollow structure. This prevents to the greatest extent the risk of thermal overstressing of the hollow structure both in the area of the junction to the feed connection and in the area of the fluid-carrying wall parts. However, even if the measures are used individually, depending on the application, they can provide a satisfactory solution. The shaping of the end area of the feed connection is not necessary, for instance, if the fluid is fed into a wide hollow space, so that the wall of the hollow structure opposite the feed connection is remote. In contrast, if the hollow structures are particularly narrow, it may only be necessary to take the measure along the end area of the feed connection, while heat conduction at the feed connection remains non-critical.
In a further embodiment of the invention, the end area of the feed connection is formed by a pipe segment, which is provided with outlet openings along the sides around which the fluid flows. The cross section of the pipe segment need not be circular; various cross sectional shapes are feasible. The pipe segment can be produced by injection molding. Another option is to produce it from a tubular semi-finished product that is deflected. In this case, the openings have to be created, for instance, by stamping. The pipe segment is furthermore provided with a plug-in connection by means of which it can be pushed onto the feed connection. This makes it also possible to retrofit this component to an existing intake system.
According to a further embodiment of the invention, the pipe segment is open at its end. This is useful in an embodiment of the pipe segment made of a tubular semi-finished product. The open pipe end serves as an additional intake opening for the recirculated exhaust gas.
An alternative fluid feed duct consists of three structural function areas: the hollow structure, the feed connection and the joint structure. The hollow structure is suitable for transmitting a fluid and can, for instance, consist of an intake pipe for an internal combustion engine. The feed connection is suitable for connection to a feed line with the introduced hot fluid being conducted through the feed line. Provided in addition is a joint structure, which on the one hand serves to mount the feed connection to the wall of the hollow structure and on the other hand provides a seal between these two components.
The described fluid feed duct must be designed to withstand the thermal stresses caused by the introduction of the hot fluid. This means that the feed connection must be heat resistant to the introduced fluid. Materials with a lower melting point, however, e.g., plastics, are frequently used for the hollow structure. Since the introduced fluid heats the feed connection to a high temperature, the junction between the feed connection and the hollow structure must be sufficiently insulated so that the hollow structure is not subject to excessive thermal stressing in this area. This is why the joint structure is provided, so that heat from the feed connection is conducted to the hollow structure via this joint structure. A temperature gradient in the joint structure is established starting from the feed connection toward the hollow structure, so that the contact surface between the joint structure and the hollow structure is cooler than the feed connection.
According to the invention, the temperature is further lowered at the junction between the hollow structure and the joint structure by providing means to prevent heat from being conducted from the feed connection to the joint structure. This naturally also reduces the thermal stressing of the junction between the joint structure and the hollow structure. This achieves higher exhaust gas recirculation rates than would be possible in a fluid feed duct without means for reducing such heat transfer. The required exhaust gas recirculation rates for diesel engines can in part be as high as 60%, which in a plastic intake tract is possible only if the aforementioned means are being used.
According to one advantageous embodiment of the invention, the means for reducing the heat transfer from the feed connection is made of ceramic. This material is sufficiently heat resistant against the introduced hot fluid. The thermal conductivity of ceramics, however, is substantially lower than that of the metallic materials typically used for the feed connection. The feed connection thus acts as a thermal insulator, so that a smaller amount of heat is transferred to the joint structure.
It is advantageous if the joint structure is also made of ceramic. This prevents excessive heat conduction in this area as well. The feed connection and the joint structure can be made as a single part, which advantageously lowers the production costs.
A further embodiment of the means for reducing heat transfer consists of a double-wall design of the feed connection. The feed connection has an inner wall and an outer wall and the fluid located in the gap between these two walls acts as an insulator. The introduced fluid is guided through the cross section formed by the inner wall.
To use the gap as an insulator to reduce heat transfer to the joint structure, the joint structure is mounted to the outer wall of the feed connection. The insulating effect of the gap can be enhanced if the described embodiment of the invention is combined with the ejector effect, which is known from the prior art. This results in a continuous exchange of the fluid within the gap and prevents it from being heated. Consequently, the outer wall remains cooler, so that less heat is being transferred to the joint structure.
According to a modification of the invention, it is also possible to influence the temperature gradient in the joint structure. This is accomplished by using means for enlarging the surface of the joint structure. This increases the amount of heat being radiated, which is proportional to the surface of the joint structure, so that the junction between the joint structure and the hollow structure heats up less. To enlarge this surface, the joint structure can be made, for instance, of thin sheet metal, which is given a bellows-type structure. The corrugated walls of this bellows-type structure provide sufficient rigidity and simultaneously enlarge the surface. Another option is to use a dish-type design of the joint structure, in which case the outer radius of the dish is selected larger than would be necessary to install the feed connection. This dish can also be made of thin sheet metal and stiffened by beads. The beads simultaneously cause the surface to be further increased.
For large-scale production, the joint structure, according to an advantageous embodiment of the inventive concept, is constructed as a bayonet lock. This creates a module that can be simply integrated into hollow structures. Particularly if the hollow structures are made of synthetic resin material, the corresponding recess, as the counter part of the bayonet lock, can be simply integrated into the wall structure. The feed connection and the joint structure can then be designed as a standard component, so that high numbers of units can be achieved. This increases the economic efficiency of the solution. The bayonet lock makes it easy to mount the fluid feed duct, and the reduced assembly costs further increase the economic efficiency of the fluid feed duct.
The described embodiments are suitable to reduce the thermal stressing of the junction between the feed connection and the hollow structure, so that in proportion to the transmitted fluid a higher amount of hot fluid can be introduced. In the application as an exhaust gas recirculation device, this means higher exhaust gas recirculation rates in the intake air for combustion. This implies not only higher thermal stressing of the junctions but also of the remaining hollow structure since the recirculated fluid inside the hollow structure cools along the walls of the hollow structure. As a result, the thermal stress limits of the hollow structure can be exceeded in these areas as well. This is the case particularly if the recirculated fluid stream can strike the wall of the hollow structure unhindered.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either alone or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.